Through the wash fabric conditioning products are often sold in liquid form. The liquid may be provided in bulk such that one package will contain multiple doses. Consumers will open the package and meter doses into the washing machine and/or laundry liquor as needed.
Although widely used, bulk liquid product forms may have associated issues in terms of packaging, storage, transportation and/or convenience of use. For example, liquid fabric conditioning products are typically sold in bottles which may add significant cost to the finished product. Additionally, liquid fabric conditioning products may comprise a substantial amount of water in the formula. The high water content increases the bulk of the product which may in turn adversely impact the associated shipping and storage costs. Additionally, liquid laundry conditioning products can be messy. This messiness may cause inconvenience to the consumer when attempting to meter out an accurate dose as it may result in drips and residue on the outside of the bottle as well as in the dispenser of the washing machine.
Liquid fabric conditioning formulations may also be characterized by physical stability challenges including, but not limited to, phase separation, gelling and creaming, any of which may lead to a shorter shelf life. The chemical stability of diester quaternary ammonium fabric softening actives in liquid formulations may be particularly challenging due to ester hydrolysis which may be dependent upon conditions including, but not limited to, pH and temperature.
Compatibility of other actives in a liquid fabric conditioning formula can be challenging due to for example: differences in the optimum pH of the actives; poor solubility of the active leading to precipitation in the product; chemical instability of the active such as via hydrolysis or cross-linking; and/or polymer-polymer interactions which may lead to undesirable rheological aesthetics such as stringiness or gelling of the product.
The aforementioned issues may be addressed by providing a liquid fabric conditioning formulation in the alternative form of a porous dissolvable solid structure containing little or no water. For example, such an article could be packaged as a single unit or in multiple units and shipped at a lower cost as compared to the traditional liquid form equivalent. Such an article could eliminate the difficulty and mess associated with handling a liquid fabric conditioning formulation since no metered pouring would be required. Moreover, many of the stability issues of the liquid form would be eliminated via physical separation such that actives could be combined in new ways that were heretofore impractical and/or impossible.
However, for porous dissolvable solid structures to be a practical form in which to supply a liquid fabric conditioning composition to the consumer, several further challenges must be addressed. For example, it may be required that a relatively high activity of fabric softening active such as a diester quaternary ammonium compound be incorporated into the foams at a high enough density such that the amount of fabric softening active that is delivered is sufficient to soften the clothes. In this way, the use of a porous dissolvable solid structure provides several advantages over the like use of a film. For example, the relatively higher surface area of the porous dissolvable solid structure allows for much higher loading of fabric softening active since this type of substrate rapidly dissolves in the washing machine or hand rinse applications, particularly those in which the water volume may be small and the water temperature may be cold (for example, under rinse conditions in 3 minutes using 15° C. water).
Yet the amount of fabric softening active incorporated into a porous dissolvable solid structure, and/or the dry density of the substrate, may require impractical dimensions of the substrate in order to deliver an effective dose to the washing machine and/or the hand rinse apparatus. For example, the open cell dissolvable substrate described as having a dry density range of 0.06 g/cm3 to about 0.10 g/cm3 in U.S. patent application Ser. No. 12/361,634, may not be practical for a fabric care application because it would require a large size dissolvable porous substrate that may be difficult to handle, or might not fit into the dispensing drawer of a front-loading washing machine. For example, a dissolvable porous substrate with a density of 0.10 g/cm3 and a thickness of 0.8 cm with a diester quaternary ammonium compound activity of 40% would require a 12.5 cm×12.5 cm size foam to deliver a dose of quat of 5 g as calculated according to the equations below:(g Quat/dose)/(% Quat activity in porous substrate)=g dissolvable porous substrate  (eq 1)(g dissolvable porous substrate)/(dry density (g/cm3))=volume dissolvable porous substrate  (eq 2)volume dissolvable porous substrate/thickness=area dissolvable porous substrate  (eq 3)
Likewise, a dissolvable porous substrate with a density of 0.06 g/cm3 and a thickness of 0.8 cm with a Quat activity of 40% would require a 16 cm×16 cm size foam to deliver 5 g of Quat active to the wash.
Dissolvable films are known comprising water-soluble polymeric structurant and a surfactant or other active component. However, in order to achieve the requisite rapid dissolution rates needed for consumer convenience, these films are generally on the order of less than 100 microns thickness (typically 50 microns) and, thereby, are generally of too low a basis weight (typically 50-100 grams of solid per square meter) to enable feasible consumer application of a sufficient dosage.
Freeze-dried open-celled porous solids for personal care have been taught (See U.S. Pat. No. 6,106,849 and US 2007/0225388). However, such resulting freeze-dried porous solids are rigid, brittle and fragile and without plasticization of the polymer such that it remains in its glassy state to avoid collapse of the structure during the process (See U.S. Pat. No. 5,457,895 Kearney P. et. al., issued 1995). Also, freeze-drying is a relatively high energy and costly process.
Based upon the foregoing, a need exists for a flexible, bendable, and soft to the touch, dissolvable porous solid structure which can be easily and quickly formulated and manufactured and that provides the properties of flexibility, dissolution and fabric conditioning desired by consumers. Such a structure should be provided to the consumer in a size that is easy to dose such as in the drawer of a front-loading washing machine, or easy to dose in a sachet for a hand-rinsing application.